Magnetic tape drive having direct drive motor and extended head travel

ABSTRACT

A magnetic tape drive having a motor with a magnetically shielded cavity or hole in one cover of the motor providing additional room for movement of a magnetic head. The cavity eliminates a mechanical interference problem, enabling direct drive of a roller (puck) combined with short overall drive height. In motors having an internal stator, some of the stator poles are eliminated and a magnetically shielded cavity is provided in the area where the stator poles are eliminated. In motors having an external stator, no stator modification is required and a shielded cavity provides access into an open area of the rotor. In addition, for motors having an external stator and sufficient magnetic shielding, a simple hole in one cover of the motor may be sufficient rather than a magnetically shielded cavity.

This is a divisional of application Ser. No. 08/639,535 filed on Apr.29, 1996, now U.S. Pat. No. 5,712,745, which is a continuation ofapplication Ser. No. 08/528,180 filed on Sep. 14, 1995, now abandoned,which is a continuation of application Ser. No. 08/282,126 filed on Jul.28, 1994, now abandoned.

FIELD OF INVENTION

This invention relates generally to magnetic tape drives and morespecifically to capstan drive motors and magnetic head positioning.

BACKGROUND OF THE INVENTION

In 1972, a belt driven tape cartridge design (U.S. Pat. No. 3,692,255,issued to Robert A. Von Behren) was introduced for use in the computerindustry for digital tape recording. Cartridges commonly in use in 1972were approximately 100 mm by 150 mm and the magnetic tape was 6.35 mm(0.250 inches) wide. Cartridges of that size and corresponding drivemechanisms are still commercially available. In 1976, smaller datacartridges were developed, as described by Alan J. Richards, Mini DataCartridge: A Convincing Alternative for Low-Cost, Removeable Storage,Hewlett-Packard Journal, May, 1976. The mini-cartridge size is 63.5 mmby 82.5 mm. Versions of the mini-cartridge are commercially availablefrom a variety of vendors with tape widths varying from 3.81 mm (0.150inches) to 6.35 mm (0.250 inches). New versions of mini-cartridges havebeen proposed having a tape width of 8.00 mm (0.315 inches). Theexternal dimensions of the proposed cartridges are identical to existingmini-cartridges but there are numerous internal changes to accommodatewider tape.

Both sizes of cartridges described above have two openings in oneedgewall. The first opening provides access to the tape by a magnetichead. The magnetic head travels across the width of the tape, transverseto the direction of tape movement, accessing one track at a time forreading or writing. The second opening provides access to a drivenroller (capstan) inside the cartridge by an external driving roller(puck) in the drive mechanism. The external driving roller (puck) isrotated by a motor in the drive mechanism. In full height drives andhalf-height drives, the external driving roller (puck) is typicallydriven directly by the drive motor. As drive height decreases, there maybe a mechanical interference between the drive motor and the magnetichead. The interference problem is made even worse with the proposedcartridges having a tape width of 8.00 mm (0.315 inches), increasing thedistance the magnetic head has to travel. Therefore, in newer shorterheight drives, the drive motor is typically displaced relative to thedriving roller (puck) and connected to the driving roller (puck) by abelt or an intermediate roller. For example, see U.S. Pat. No. 5,210,664issued to Mark W. Perona on May 11, 1993. Belts and intermediate rollersadd cost and may slip or cause other speed problems. A direct drive isdesirable as the lowest cost and most reliable way of connecting thedrive motor to the driving roller (puck). A drive mechanism is neededthat has both a directly driven roller (puck) and room for full movementof the magnetic head.

SUMMARY OF THE INVENTION

A tape drive mechanism is provided having a directly driven drive roller(puck) and room for full movement of the magnetic head. Two embodimentsare provided, a first embodiment with drive motors having an externalstator and a second embodiment with drive motors having an internalstator. In drives having a drive motor with an internal stator, part ofthe stator is removed and a magnetically shielded area is provided inthe evacuated stator area for head travel. In some drives having a drivemotor with an external stator, a simple hole is provided in the motorcover to permit the head to travel into the motor cup.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a tape cartridge and chassis.

FIG. 2A is a top view of a portion of the tape cartridge and chassis ofFIG. 1.

FIG. 2B is a side view of a portion of the tape cartridge and chassis ofFIG. 2.

FIG. 3A is a cross section of a motor having an internal stator.

FIG. 3B is a cross section of a motor having an external stator.

FIG. 4 is a perspective view of a motor having an internal stator with afirst alternative for a portion removed to accommodate travel of themagnetic head.

FIG. 5 is a perspective view of a motor having an internal stator with asecond alternative for a portion removed to accommodate travel of themagnetic head.

FIG. 6 is a perspective view of a motor having an internal stator with athird alternative for a portion removed to accommodate travel of themagnetic head.

FIG. 7 is a perspective view of a motor having an external stator withan opening inside the rotor to accommodate travel of the magnetic head.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

FIG. 1 illustrates a tape cartridge 100 inserted in a drive 102. Amagnetic tape 104 in the tape cartridge 100 is in contact with amagnetic head 106 in the drive 102. A driven roller (capstan) 108 in thetape cartridge is in contact with a driving roller (puck) 110 in thedrive 102. The driving roller (puck) 110 is driven by a motor 112.

FIG. 2A is a top view of the components illustrated in FIG. 1. As inFIG. 1, the magnetic tape 104 in the tape cartridge 100 is in contactwith the magnetic head 106 in the drive 102. The driven roller (capstan)108 in the tape cartridge is in contact with the driving roller (puck)110 in the drive 102. The driving roller (puck) 110 is driven by themotor 112. Note that in the configuration illustrated in FIG. 2, themotor 112 extends beyond the head 106 so that movement of the head 106is potentially constrained, depending on the height of the variouscomponents.

FIG. 2B is a side view of just the tape 104, the head 106 and a portionof the motor 112. As illustrated in FIG. 2B, the direction of movementof the head 106 is as depicted by the double-ended arrow 200. If themotor 112 extends below the head 106 as in FIG. 2B, the motor 112 limitsthe distance the head 106 can travel. Providing the required head travellimits the height of the overall drive mechanism. In the invention, thehead 106 is permitted to travel into the body of the motor, either intoa magnetically shielded area such as a cavity or depression as depictedby dashed line 202 or through a simple hole in a top cover of the motor.

FIGS. 3A and 3B illustrate simplified cross sections of a type of motorcommonly used in tape and disk mechanisms. For purposes of illustration,the motors in FIGS. 3A and 3B are depicted as three-phase brushless DCmotors having 12 stator poles, but other variations of numbers of phasesand numbers of poles are equally suitable. In FIG. 3A, a stator 300 hascoils of wire (not illustrated) wound around magnetic poles to formelectromagnets. A rotor 302 has multiple permanent magnetic areas. Therotor 302 is connected by a cup shaped cover to an internal shaft 304.Note in FIG. 3A that the illustrated stator has 12 stator poles labeledA₁ -A₄, B₁ -B₄ and C₁ -C₄. The stator poles are wired so that there arefour poles (for example A₁ -A₄) for each of three electrical phases(A,B,C). All poles for each electrical phase are wired together. Forexample, for phase A, poles A₁ -A₄ are all energized. As each phase issequentially energized, the permanent magnetic areas in the rotorfollow. For example, in FIG. 3A, electromagnetic poles A₁ -A₄ may beenergized so that opposite polarity permanently magnetized areas in therotor 302 are aligned with each of the phase A poles. Then, if poles A₁-A₄ are turned off and poles B₁ -B₄ are energized, the rotor 302 willrotate clockwise to align with the phase B poles. Likewise, poles B₁ -B₄may then be turned off and poles C₁ -C₄ energized.

In the invention, for internal stator motors as illustrated in FIG. 3A,the motor is constructed with a stator in which selective motor polesare eliminated to make room for head travel. If a single pole (forexample pole A₁ (312)) is eliminated, the motor will still rotate butone electrical phase (for example phase A) will have less torque thanthe other two phases. To ensure torque balance, an equal number of polesfrom each of the electrical phases must to be eliminated. Therefore, ifpole A₁ is eliminated, then one member of the set of poles B₁, B₂, B₃and B₄ must be eliminated and one member of the set of poles C₁, C₂, C₃and C₄ must be eliminated. Three adjacent poles may be eliminated, forexample A₁ (312), B₁ (314) and C₁ (316). Clearly, other combinations arealso possible, such as A₁ (312), C₁ (316), B₂ (318) or A₁ (312), B₂(318), C₃ (320). In each of the combinations, the rotational torque isbalanced but there are asymmetrical forces on the rotor causing someforce on the bearings transverse to the direction of rotation. Withadequate bearings, there is no significant wobble of the rotor 302.

FIG. 3B illustrates a motor having an external stator 306, an internalrotor 308, and the internal rotor attached to a central shaft 310. Aswill be discussed below in conjunction with FIG. 7, an external statormotor can be modified to accommodate additional head travel withoutrequiring modification of the stator.

FIG. 4 illustrates a motor with an internal stator as in FIG. 3A andwith three adjacent poles eliminated. That is, FIG. 4 corresponds toelimination of A₁ (312), B₁ (314) and C₁ (316) in FIG. 3A. Note in FIG.4 that a cup 400 connects the rotor 302 to the central shaft 304. FIG. 4also illustrates a bearing assembly 402. In conjunction with theinvention, the motor is covered with a top cover 404 made of a materialsuch as steel or other material capable of isolating the magnetic headfrom electromagnetic fields inside the stator 300. A cavity ordepression 406 (corresponding to FIG. 2B, 202) is formed in the topcover 404 to permit the magnetic head to travel into the stator areawhere the poles have been eliminated. The area for receiving the head isdepicted as a formed depression 406, but a metal cylinder or box with anenclosed end or any other magnetically shielded shape may be used aslong as the head can penetrate into the body of the motor and as long asthe area for receiving the head does not interfere with operation of themotor.

FIGS. 5 and 6 illustrate a motor as in FIG. 4 but with differentcombinations of stator poles eliminated. FIG. 5 corresponds toelimination of every other pole such as poles A₁ (312), C₁ (316), B₂(318) in FIG. 3A. FIG. 6 corresponds to elimination of every fourth polesuch as poles A₁ (312), B₂ (318), C₃ (320) in FIG. 3A.

FIG. 7 illustrates an external stator motor as in FIG. 3B. Asillustrated in FIG. 7, a cup 700 inside the rotor 308 connects the rotor308 to the central shaft 304. FIG. 7 also illustrates a bearing assembly702. Typically, the cup 700 is made of a material such as steel thatisolates the interior of the cup 700 from electromagnetic fieldsresulting from permanent magnetic areas of the rotor 308 and from thestator 306. Therefore, for an external stator of sufficient diameter andsufficient shielding, a simple hole 706 in the top cover 704 permits themagnetic head to travel into the interior of the motor. No modificationof the stator 306 is required. If the cup 700 does not provide adequateshielding, a formed cavity or depression may be used as in FIG. 4, 406.

The foregoing description of the present invention has been presentedfor purposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise form disclosed, andother modifications and variations may be possible in light of the aboveteachings. The embodiment was chosen and described in order to bestexplain the principles of the invention and its practical application tothereby enable others skilled in the art to best utilize the inventionin various embodiments and various modifications as are suited to theparticular use contemplated. It is intended that the appended claims beconstrued to include other alternative embodiments of the inventionexcept insofar as limited by the prior art.

What is claimed is:
 1. A magnetic tape drive comprising:a magnetic head,the magnetic head being moveable with a range of movement; a motor,adjacent to the magnetic head the motor including a rotor and a stator,the stator positioned external to the rotor, the rotor having a plane ofrotation; a rotating cup in the motor, attached to the rotor, having anopen area towards the magnetic head; a cover on the motor, between theopen area of the rotating cup and the magnetic head; and a hole in thecover, the hole positioned so that at least part of the range ofmovement of the magnetic head is through the hole and into the open areaof the rotating cup in the motor, transverse to the plane of rotation ofthe rotor, thereby reducing a dimension of the magnetic tape drivetransverse to the plane of rotation of the rotor.
 2. A magnetic tapedrive as in claim 1 further comprising:the tape drive adapted to receivea tape cartridge having a drive roller internal to the tape cartridge,the drive roller being driven directly by the motor.